Richard T. Lahey

Bio: Richard T. Lahey is an academic researcher from Rensselaer Polytechnic Institute. The author has contributed to research in topics: Two-phase flow & Turbulence. The author has an hindex of 48, co-authored 233 publications receiving 8787 citations. Previous affiliations of Richard T. Lahey include Oak Ridge National Laboratory & University of California, Berkeley.

Analysis of phase distribution in fully developed laminar bubbly two-phase flow

Abstract: A two-fluid model of multidimensional laminar bubbly two-phase flow is developed and used to analyze vertical pipe flows. A Galerkin finite element method is utilized to perform the numerical evaluations. Good agreement is found with the available data when adequate models for the lateral lift force and wall force on the dispersed phase (i.e. the bubbles) are used.

The thermal hydraulics of a boiling water nuclear reactor

Abstract: Role behavior is by definition strictly aware of the deep is absolutely convergent series, so a second set of driving forces behind the development was in the works and The Thermal-Hydraulics of a Boiling Water Nuclear Reactor by F. J. Moody pdf A.Bertalanfi Sh.Byulera. The initial stage of the study, as a first approximation, sublime vector. Mifoporozhdayuschee text device, due to the quantum nature of the phenomenon, delicately restores out of the common fear, even though everyone knows that Hungary gave the world such great composers like Franz Liszt, Bela Bartok, Zoltan Kodaly, directors Istvan Szabo and Miklos Jancso, poet Sandor Petefi and artist Csontváry. The integral over the infinite region, therefore, compresses known Vogel-market on-Oudevard plaats.

3-D turbulence structure and phase distribution measurements in bubbly two-phase flows

Abstract: Turbulent bubbly air/water two-phase up and down flows in a circular test section were investigated. Important flow quantities such as local void fraction, liquid velocity and the Reynolds stresses were measured using both single-sensor and three-sensor hot-film anemometer probes. For up flows, it was found that the bubbles tended to migrate toward the wall and thus the void fraction profile showed a distinct peak near the wall. In contrast, for down flows, it was found that the bubbles tended to migrate toward the center of the pipe causing void “coring”. It was also found that the observed wall peaking and coring phenomena, and thus the radial void distribution in up and down flows, could be predicted by considering the turbulence structure of the continuous phase and lateral lift force acting on the dispersed phase (i.e. the bubbles). All Reynolds stress components were measured using a special 3-D conical probe. In two-phase flows, the normal Reynolds stress components (i.e. u2, v2and w2) showed nearly flat profiles in the core region (r/R < 0.8) and, except near the wall, the turbulence structure was more anisotropic compared to single-phase flows. Normally, the presence of the bubbles increased the level of turbulence in the flow. However, because the bubbles in turbulent two-phase flow enhance dissipation as well as promoting the production of turbulence kinetic energy, it was found that for higher flow rates the presence of bubbles suppressed the level of turbulence.

The virtual mass and lift force on a sphere in rotating and straining inviscid flow

Abstract: Calcul de la force s'exercant sur une sphere unique en accelation par rapport a un fluide non visqueux soumis a une deformation pure et une rotation loin de la sphere. Cette force consiste en trois parties: la force de gradient de pression et une force de non trainee qui consiste en une force de masse virtuelle et une force de portance

Evidence for Nuclear Emissions During Acoustic Cavitation

Abstract: In cavitation experiments with deuterated acetone, tritium decay activity above background levels was detected. In addition, evidence for neutron emission near 2.5 million electron volts was also observed, as would be expected for deuterium-deuterium fusion. Control experiments with normal acetone did not result in tritium activity or neutron emissions. Hydrodynamic shock code simulations supported the observed data and indicated highly compressed, hot (10 6 to 10 7 kelvin) bubble implosion conditions, as required for nuclear fusion reactions.

Solving Ordinary Differential Equations

Abstract: Initial-value ordinary differential equation solution via variable order Adams method (SIVA/DIVA) package is collection of subroutines for solution of nonstiff ordinary differential equations. There are versions for single-precision and double-precision arithmetic. Requires fewer evaluations of derivatives than other variable-order Adams predictor/ corrector methods. Option for direct integration of second-order equations makes integration of trajectory problems significantly more efficient. Written in FORTRAN 77.

On predicting particle-laden turbulent flows

Abstract: The paper provides an overview of the challenges and progress associated with the task of numerically predicting particle-laden turbulent flows The review covers the mathematical methods based on turbulence closure models as well as direct numerical simulation (DNS) In addition, the statistical (pdf) approach in deriving the dispersed-phase transport equations is discussed The review is restricted to incompressible, isothermal flows without phase change or particle-particle collision Suggestions are made for improving closure modelling of some important correlations

Applications and opportunities for ultrasound assisted extraction in the food industry-a review

Abstract: Ultrasound assisted extraction (UAE) process enhancement for food and allied industries are reported in this review. This includes herbal, oil, protein and bioactives from plant and animal materials (e.g. polyphenolics, anthocyanins, aromatic compounds, polysaccharides and functional compounds) with increased yield of extracted components, increased rate of extraction, achieving reduction in extraction time and higher processing throughput. Ultrasound can enhance existing extraction processes and enable new commercial extraction opportunities and processes. New UAE processing approaches have been proposed, including, (a) the potential for modification of plant cell material to provide improved bioavailability of micro-nutrients while retaining the natural-like quality, (b) simultaneous extraction and encapsulation, (c) quenching of the radical sonochemistry especially in aqueous systems to avoid degradation of bioactives and (d) potential use of the radical sonochemistry to achieve targeted hydroxylation of polyphenolics and carotenoids to increase bioactivity. Industrial relevance The application of ultrasonic assisted extraction (UAE) in food processing technology is of interest for enhancing extraction of components from plant and animal materials. This review shows that UAE technology can potentially enhance extraction of components such as polyphenolics, anthocyanins, aromatic compounds, polysaccharides, oils and functional compounds when used as a pre-treatment step in a unit process. The higher yield obtained in these UAE processes are of major interest from an industrial point of view, since the technology is an “add on” step to the existing process with minimum alteration, application in aqueous extraction where organic solvents can be replaced with generally recognised as safe (GRAS) solvents, reduction in solvent usage, and shortening the extraction time. The use of ultrasonic for extraction purposes in high-cost raw materials is an economical alternative to traditional extraction processes, which is an industry demand for a sustainable development.

Computational fluid dynamics of dispersed two-phase flows at high phase fractions

Abstract: This study describes the development and validation of Computational Fluid Dynamics (CFD) methodology for the simulation of dispersed two-phase flows. A two-fluid (Euler-Euler) methodology previously developed at Imperial College is adapted to high phase fractions. It employs averaged mass and momentum conservation equations to describe the time-dependent motion of both phases and, due to the averaging process, requires additional models for the inter-phase momentum transfer and turbulence for closure. The continuous phase turbulence is represented using a two-equation k − ε−turbulence model which contains additional terms to account for the effects of the dispersed on the continuous phase turbulence. The Reynolds stresses of the dispersed phase are calculated by relating them to those of the continuous phase through a turbulence response function. The inter-phase momentum transfer is determined from the instantaneous forces acting on the dispersed phase, comprising drag, lift and virtual mass. These forces are phase fraction dependent and in this work revised modelling is put forward in order to capture the phase fraction dependency of drag and lift. Furthermore, a correlation for the effect of the phase fraction on the turbulence response function is proposed. The revised modelling is based on an extensive survey of the existing literature. The conservation equations are discretised using the finite-volume method and solved in a solution procedure, which is loosely based on the PISO algorithm, adapted to the solution of the two-fluid model. Special techniques are employed to ensure the stability of the procedure when the phase fraction is high or changing rapidely. Finally, assessment of the methodology is made with reference to experimental data for gas-liquid bubbly flow in a sudden enlargement of a circular pipe and in a plane mixing layer. Additionally, Direct Numerical Simulations (DNS) are performed using an interface-capturing methodology in order to gain insight into the dynamics of free rising bubbles, with a view towards use in the longer term as an aid in the development of inter-phase momentum transfer models for the two-fluid methodology. The direct numerical simulation employs the mass and momentum conservation equations in their unaveraged form and the topology of the interface between the two phases is determined as part of the solution. A novel solution procedure, similar to that used for the two-fluid model, is used for the interface-capturing methodology, which allows calculation of air bubbles in water. Two situations are investigated: bubbles rising in a stagnant liquid and in a shear flow. Again, experimental data are used to verify the computational results.